Process and electrolyte for depositing lead and lead-containing layers

ABSTRACT

A process for acidic electrolytical deposition of lead layers and predominantly lead-containing layers onto surfaces using an electrolyte containing lead salts and acids, in particular alkanesulfonic acid, borofluoric acid or silicofluoric acid, with non-ionic surfactants and cationic or amphoteric surfactants being added to the electrolyte. The process can be operated at current densities of from 0.5 to 20 A/dm 2  and at a pH value below 1.

The present invention relates to a process for acidic electrolyticaldeposition of lead layers and predominantly lead-containing layers ontosurfaces using an electrolyte containing lead salts and acids, inparticular alkanesulfonic acid, borofluoric acid or silicofluoric acid.Furthermore, the present invention relates to an electrolyte forperforming the process and the use of surfactants in acidic leadelectrolytes.

Processes for acidic electrolytical deposition of lead layers andpredominantly lead-containing layers are known in prior art. In theseprocesses, only lead fluorosilicate, lead fluoroborate and leadperchlorate electrolyte have been gaining special significance. To theselead electrolytes are added organic materials, e.g., gelatin, glue,peptones, phenolsulfonic acid, and waste sulfite liquor to obtainfine-grained, smooth precipitates.

Among these known electrolytes, the lead perchlorate electrolyte, inparticular, is said to have special merits:

1. good solubility.,

2. high electrical conductivity,

3. good chemical stability,

4. a 100% anodic and cathodic current efficiency,

5. smooth, dense coatings, and

6. no polarization phenomenons.

In spite of these obvious advantages, the lead perchlorate electrolytecould not gain acceptance in practice. Drawbacks of this electrolyteresult, in particular, from the dangerousness of perchlorate.

From U.S. Pat. No. 2,525,942, acidic lead electrolytes on the basis ofthe alkanesulfonate are known. The drawback of the electrolytesmentioned therein is that lead deposited therefrom forms an amorphous,non-dense, porous layer of lead. Furthermore, this electrolyte permitsdeposition only in a very narrow range of current density.

U.S. Pat. No. 4,701,244 discloses an electrolytical bath for thedeposition of tin and lead in the presence of excess (loweralkylsulfonic acid or acid salt containing the following admixtures:additives such as benzalacetone, benzaldehydes and aromatic pyridines,surface-active substances such as betaines, alkylene oxide, polymeres,imidazolinium compounds, and quaternary ammonium salts, andformaldehyde. No disclosure is made whatsoever concerning thecombination of non-ionic surfactants and cationic or amphotericsurfactants in an electrolyte for the deposition of lead layers andpredominantly lead-containing layers.

It is object of the present invention to provide a process for acidicelectrolytical deposition of lead layers and predominantlylead-containing layers onto surfaces, the merits of which resemblingthose of electrolysis using lead perchlorate without having theextraordinary dangerousness of same process.

Now, this problem is solved in surprisingly simple fashion by a processwherein the electrolyte, in addition to lead salts and acids,particularly alkanesulfonic acid, borofluoric acid or silicofluoricacid, contains non-ionic surfactants and/or cationic or amphotericsurfactants.

Using the process according to the invention, it is now possible toobtain smooth, dense and finely crystalline lead deposits even on basismaterials having gross deformations. Moreover, in the process accordingto the invention, polarization phenomenons of previously usedelectrolytes are reduced both in the anode and cathode reactions. At thesame time, better anode solubility is achieved. It is of particularadvantage that applicable cathodic current densities are higher. Thus,it is possible to operate using substantially lower electrolyte leadcontent. As a consequence, the rinsing water lead contamination is loweras well. Thus, on the whole, waste management of both lead-containingelectrolyte and rinsing water is substantially simplified.

Hence, subject matter of the present invention is a process for acidicelectrolytical deposition of lead layers and predominantlylead-containing layers onto surfaces using an electrolyte containinglead salts and acids, in particular alkanesulfonic acid, borofluoricacid or silicofluoric acid, characterized in that non-ionic surfactantsand cationic or amphoteric surfactants are added to the electrolyte.Preferably, the process according to the invention is operated atcurrent densities of from 0.5 to 20 A/dm² and at a pH value below 1. Inanother preferred embodiment of the process according to the invention,operating is done at a temperature of from 20° to 80° C., preferablyfrom 30° to 50° C. In the process according to the invention, the freeacid content is adjusted to from 50 to 150 g/l, preferably. In theprocess of the invention, operating is done at lead contents of from 10to 200 g/l, preferably. Particularly preferred is a lead content of from10 to 60 g/l. The overall concentration of non-ionic surfactants andcationic and amphoteric surfactants should be from 1 to 15 g/l.Preferably, the concentration of cationic or amphoteric surfactants isfrom 0.1 to 3 g/l.

Another object of the present invention is an electrolyte for acidicelectrolytical deposition of lead layers and pre-dominantlylead-containing layers onto surfaces, characterized in that there arecontained

a) a soluble lead salt, optionally with smaller amounts of additionalsoluble metal salts,

b) free acids such as alkanesulfonic acids, borofluoric acid orsilicofluoric acid,

c) non-ionic surfactants and cationic or amphoteric surfactants.

Preferably, the soluble lead salt and the optionally additional metalsalts are fluoroborates, fluorosilicates and/or alkanesulfonates.Especially preferred as an additional soluble metal salt is a copperand/or tin salt. Preferably, the non-ionic surfactant is an alkanol,alkylphenol, alkylamino-, arylphenol polyglycol ether, or a blockpolymerizate of ethylene oxide or propylene oxide. Where the non-ionicsurfactant is a polyglycol ether, it preferably has from 7 to 30 molesof ethylene oxide per mole. Preferably, the polyglycol ether has a C₅-C₂₀ alkanol or alkyl residue. In another electrolyte embodiment of theinvention, the amphoteric surfactant is cation-active at a pH valuebelow 1. In another preferred embodiment, a cation surfactant,preferably a quaternary ammonium compound, is present in addition to thenon-ionic surfactant.

Another object of the present invention is the use of non-ionicsurfactants and cationic or amphoteric surfactants in acidic leadelectrolytes for electrolytical deposition of lead layers andpredominantly lead-containing layers onto surfaces.

The following reference experiment as well as the examples demonstrateboth the process itself and its merits.

REFERENCE EXPERIMENT The following electrolytes were examined:Electrolyte I (prior art).

110.0 g/l of lead as lead fluoroborate

50.0 g/l of free borofluoric acid

0.2 g/l of glue.

Electrolyte II (prior art)

20.0 g/l of lead as lead alkanesulfonate

5.0 g/l of free alkanesulfonic acid

0.2 g/l of glue.

Electrolyte III (prior art)

15.0 g/l of lead as lead fluoroborate

50.0 g/l of free borofluoric acid

3.0 g/l of nonylphenol polyglycol ether with 10 moles of ethyleneoxide/mole

Electrolyte IV (according to the invention)

15.0 g/l of lead as lead fluoroborate

50.0 g/l of free borofluoric acid

3.0 g/l of nonylphenol polyglycol ether with 10 moles of ethyleneoxide/mole

0.5 g/l dodecyldimethylbenzylammonium chloride

Electrolyte V (according to the invention)

20.0 g/l of lead as lead fluorosilicate

50.0 g/l of free silicofluoric acid

5.0 g/l of coconut fatty alcohol polyglycol ether with 13 moles ofethylene oxide/mole

1.0 g/l of (ditallow fatty alkyl)dimethylammonium chloride

Electrolyte VI (according to the invention)

60.0 g/l of lead as lead alkanesulfonate

100.0 g/l of free alkanesulfonic acid

7.0 g/l of synthetic alcohol polyglycol ether with 15 moles of ethyleneoxide/mole

1.0 g/l of doecyldimethylbenzylammonium chloride

Electrolyte VII (according to the invention)

20.0 g/l of lead as lead alkanesulfonate

70.0 g/l of free alkanesulfonic acid

5.0 g/l of β-naphthol polyglycol ether with 9 moles of ethyleneoxide/mole

1.0 g/l of TRITON QS 15 (amphoteric surfactant by company Rohm & Haas)

The above electrolytes were subjected to electrolysis in a Hull cellhaving brass sheets. Electrolysis was done at a cell current of 1.5 Afor 10 minutes at room temperature with gentle stirring using a magneticstirrer.

Using electrolytes according to prior art, only dark and grey leadprecipitates could be obtained. In addition, with electrolyte I thesheet was amorphously burnt at high current density range. Withelectrolyte II, only the first 2 cm were covered with a dark amorphouslayer. From about 5 cm on, deposition did no longer occur. At highcurrent density range, electrolyte III showed burning in the form of adark amorphous deposit.

Using electrolytes IV to VI of the invention, a uniformly bright andfinely crystalline precipitate having very broad covering on thebackside was found.

EXAMPLE 1

By co-precipitation of, for example, tin and/or copper, the process ofthe invention is conveniently suited for providing solderable layers onsurfaces (lead with portions of from 5 to 15% of tin). For this purpose,an electrolyte having the following composition was used for theelectrolytical coating of a brass sheet using the same conditions as inthe reference experiment:

20.0 g/l of lead as lead fluoroborate

2.0 g/l of tin as tin fluoroborate

50.0 g/l of free borofluoric acid

2.0 g/l of β-naphthol polyglycol ether with 12 moles of ethyleneoxide/mole

0.5 g/l of dodecyldimethylbenzylammonium chloride

The finely crystalline and bright precipitate was found to beexcellently solderable. Analysis of the removed and analyzed metalcoating revealed a content of 88% by weight of lead and 12% by weight oftin.

EXAMPLE 2

Also of special interest are lead-containing inlet layers on slidebearings (lead with 10% of tin and 3% of copper). Here, an electrolyteof following composition at a current density of about 10 A/dm² was usedfor coating bearing shells having an inlet layer of about 30 μmthickness.

50.0 g/l of lead as lead alkanesulfonate

10.0 g/l of tin as tin alkanesulfonate

4.0 g/l of copper as copper alkanesulfonate

70.0 g/l of free alkansulfonic acid

8.0 g/l of nonylphenol polyglycol ether with 14 moles of ethyleneoxide/mole

1.5 g/l of dodecyldimethylbenzylammonium chloride

Electrolysis furnished a finely crystalline and bright precipitate.Analysis of the precipitate revealed 85% of lead, 11% of tin and 4% ofcopper.

We claim:
 1. A process for electrolytical deposition of lead layers andpredominantly lead-containing layers from acidic solutions onto surfacesusing an electrolyte consisting essentially of an alkanesulfonate saltof lead, an acid selected from the group consisting of alkanesulfonicacid, borofluoric acid, and silicofluoric acid, and an agent selectedfrom the group consisting of a cationic surfactant, an amphotericsurfactant, a mixture of a nonionic surfactant and cationic surfactant,and a mixture of a nonionic and amphoteric surfactant, and wherein theelectrolyte is maintained at a pH less than
 1. 2. The process of claim 1wherein the deposition is carried out at current densities of from 0.5to 20 A/dm².
 3. The process of claim 1 wherein deposition is carried outat a temperature of from 20° to 80° C.
 4. The process of claim 1 whereindeposition is carried out at a temperature of from 30°-50° C.
 5. Theprocess according to claim 1 wherein the electrolyte has a free-acidcontent of from 50-150 g/l.
 6. The process according to claim 1 whereinthe electrolyte has a lead content of from 10 to 200 g/l.
 7. The processof claim 1 wherein the electrolyte has a lead content of from 10 to 60g/l.
 8. The process of claim 1 wherein the agent is a mixture of anonionic surfactant and a cationic surfactant or a mixture of a nonionicsurfactant and an amphoteric surfactant at a concentration of 1 to 15g/l.
 9. The process of claim 1 wherein the agent is a cationicsurfactant or an amphoteric surfactant at a concentration of 0.1 to 3g/l.
 10. A process for electrolytical deposition according to claim 1wherein the acid is an alkanesulfonic acid.
 11. An electrolyte foracidic electrolytical deposition of lead layers and predominantlylead-containing layers onto surfaces consisting essentially of:a) asoluble alkanesulfonate lead salt; b) a free acid selected from thegroup consisting of alkanesulfonic acid, borofluoric acid, andsilicofluoric acid; and c) an agent selected from the group consistingof a nonionic surfactant, a cationic surfactant, an amphotericsurfactant, a mixture of a nonionic surfactant and a cationicsurfactant, and a mixture of a nonionic surfactant and an amphotericsurfactant; maintained at a pH less than
 1. 12. The electrolyte of claim11 further comprising a soluble metal salt.
 13. The electrolyte of claim11 further consisting of a soluble copper salt, a soluble tin salt, or acombination thereof, the weight percent of the copper salt, tin salt, orcombination thereof being substantially less than the weight percent ofthe lead salt.
 14. The electrolyte of claim 11 wherein the agentcomprises a nonionic surfactant selected from the group consisting of analkanol polyglycol ether, an alkylphenol polyglycol ether, an alkylaminopolyglycol ether, an arylphenol polyglycol ether, a blocked polymer ofethylene oxide, and a blocked polymer of propylene oxide.
 15. Theelectrolyte of claim 11 wherein the agent comprises a nonionicsurfactant selected from the group consisting of an alkanol polyglycolether, alkylphenol polyglycol ether, alkylamino polyglycol ether, andarylphenol polyglycol ether having from 7 to 30 moles of ethylene oxideper mole of the polyglycol ether.
 16. The electrolyte of claim 11wherein the agent comprises a nonionic surfactant selected from thegroup consisting of a C₅ -C₂₀ alkanol polyglycol ether, a C₅ -C₂₀alkylphenol polyglycol ether, and a C₅ -C₂₀ alkylamino polyglycol ether.17. The electrolyte of claim 11 wherein the agent comprises anamphoteric surfactant that is cation-active at a pH less than
 1. 18. Theelectrolyte according to claim 11 wherein the agent is a mixture of anonionic surfactant and a cationic surfactant.
 19. The electrolyte ofclaim 11 wherein the agent is a mixture of a cationic surfactant and anonionic surfactant, wherein the cationic surfactant is a quaternaryammonium compound.
 20. An electrolyte according to claim 11 wherein thefree acid is an alkanesulfonic acid.